Actuator failure detection systems and methods

ABSTRACT

A lift device comprises a base, a retractable lift mechanism, a work platform, a linear actuator, and a lift controller. The base has a plurality of wheels. The retractable lift mechanism has a first end coupled to the base and is moveable between an extended position and a retracted position. The work platform is configured to support a load. The work platform is coupled to and supported by a second end of the retractable lift mechanism. The linear actuator is configured to selectively move the retractable lift mechanism between the extended position and the retracted position. The lift controller is configured to monitor at least one lift characteristic associated with the linear actuator and to determine whether an actuator failure has been detected based on the at least one lift characteristic associated with the linear actuator.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/829,853, filed Apr. 5, 2019, which is incorporated herein byreference in its entirety.

BACKGROUND

Lift devices commonly include a vertically movable platform that issupported by a foldable series of linked supports. The linked supportsare arranged in an “X” pattern, crisscrossing with one another. Ahydraulic cylinder generally controls vertical movement of the platformby engaging and rotating (i.e., unfolding) the lowermost set of linkedsupports, which in turn unfold the other linked supports within thesystem. The platform raises and lowers based upon the degree ofactuation by the hydraulic cylinder. A hydraulic cylinder may alsocontrol various other vehicle actions, such as, for example, steering orplatform tilt functions. Lift devices using one or more hydrauliccylinders require an on-board reservoir tank to store hydraulic fluidfor the lifting process.

SUMMARY

One exemplary embodiment relates to a lift device. The lift devicecomprises a base, a retractable lift mechanism, a work platform, and alinear actuator. The base has a plurality of wheels. The retractablelift mechanism has a first end coupled to the base and is moveablebetween an extended position and a retracted position. The work platformis configured to support a load. The work platform is coupled to andsupported by a second end of the retractable lift mechanism. The linearactuator is configured to selectively move the retractable liftmechanism between the extended position and the retracted position. Thelinear actuator comprises a central screw rod, an electric motor, and anut assembly. The electric motor is configured to provide rotationalactuation to the central screw rod. The nut assembly comprises a primarynut mechanism and a secondary nut mechanism. The primary nut mechanismis engaged with the central screw rod and configured to translate therotational actuation of the central screw rod into translational motionto move the retractable lift mechanism between the extended position andthe retracted position. The secondary nut mechanism is disengaged fromthe central screw rod. In an event of a primary nut mechanism failure,the secondary nut mechanism is configured to engage the central screwrod.

Another exemplary embodiment relates to a lift device. The lift devicecomprises a base, a retractable lift mechanism, a work platform, alinear actuator, and a lift controller. The base has a plurality ofwheels. The retractable lift mechanism has a first end coupled to thebase and is moveable between an extended position and a retractedposition. The work platform is configured to support a load. The workplatform is coupled to and supported by a second end of the retractablelift mechanism. The linear actuator is configured to selectively movethe retractable lift mechanism between the extended position and theretracted position. The lift controller is configured to monitor atleast one lift characteristic associated with the linear actuator and todetermine whether an actuator failure has been detected based on the atleast one lift characteristic associated with the linear actuator.

Another exemplary embodiment relates to a lift device. The lift devicecomprises a base, a retractable lift mechanism, a work platform, alinear actuator, and a lift controller. The base has a plurality ofwheels. The retractable lift mechanism has a first end coupled to thebase and is moveable between an extended position and a retractedposition. The work platform is configured to support a load. The workplatform is coupled to and supported by a second end of the retractablelift mechanism. The linear actuator is configured to selectively movethe retractable lift mechanism between the extended position and theretracted position. The linear actuator comprises a central screw rod,an electric motor, and a nut assembly. The electric motor is configuredto provide rotational actuation to the central screw rod. The nutassembly comprises a primary nut mechanism and a secondary nutmechanism. The primary nut mechanism is engaged with the central screwrod and configured to translate the rotational actuation of the centralscrew rod into translational motion to move the retractable liftmechanism between the extended position and the retracted position. Thesecondary nut mechanism is disengaged from the central screw rod. In anevent of a primary nut mechanism failure, the secondary nut mechanism isconfigured to engage the central screw rod. The lift controller isconfigured to monitor at least one lift characteristic associated withthe linear actuator and to determine whether an actuator failure hasbeen detected based on the at least one lift characteristic associatedwith the linear actuator.

The invention is capable of other embodiments and of being carried outin various ways. Alternative exemplary embodiments relate to otherfeatures and combinations of features as may be recited herein.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIG. 1A is a side perspective view of a lift device in the form of ascissor lift, according to an exemplary embodiment;

FIG. 1B is another side perspective view of the lift device of FIG. 1A;

FIG. 2A is a side view of the lift device of FIG. 1A, shown in aretracted or stowed position;

FIG. 2B is a side perspective view of the lift device of FIG. 1A, shownin an extended or work position;

FIG. 3 is a side view of the lift device of FIG. 1A, depicting variousvehicle controllers;

FIG. 4 is a side view of a linear actuator of the lift device of FIG.1A;

FIG. 5 is a bottom view of the linear actuator of FIG. 4;

FIG. 6 is a side view of a push tube and a nut assembly of the linearactuator of FIG. 4;

FIG. 7 is a cross-sectional view of the nut assembly of FIG. 6;

FIG. 8A is a detail cross-sectional view of a primary nut mechanism ofthe nut assembly of FIG. 7;

FIG. 8B is a detail view of the primary nut mechanism of FIG. 8A;

FIG. 9 is a cross-sectional view of a secondary nut mechanism of the nutassembly of FIG. 6;

FIG. 10 is a flowchart detailing an exemplary lift process of the liftdevice of FIG. 1A; and

FIG. 11 is a side perspective view of another lift device in the form ofa boom lift, according to another exemplary embodiment.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the presentapplication is not limited to the details or methodology set forth inthe description or illustrated in the figures. It should also beunderstood that the terminology is for the purpose of description onlyand should not be regarded as limiting.

Referring to the figures generally, the various exemplary embodimentsdisclosed herein relate to systems, apparatuses, and methods fordetecting actuator failure on a lift device. The lift device includes alinear actuator having central screw rod, a primary nut mechanism, and asecondary nut mechanism. The secondary nut mechanism provides a failsafeor a backup nut mechanism in the event that the primary nut mechanismfails. A lift controller is additionally provided, which monitorsvarious lift characteristics to determine both whether a maximumallowable motor torque has been exceeded and whether actuator failurehas been detected. The lift controller is configured to alert anoperator in the case of an actuator failure, and to inhibit unsafeoperating conditions.

According to the exemplary embodiment depicted in FIGS. 1A and 1B, avehicle, shown as vehicle 10, is illustrated. In some embodiments, thevehicle 10 may be a scissor lift, for example, which can be used toperform a variety of different tasks at various elevations. The vehicle10 includes a base 12 supported by wheels 14A, 14B positioned about thebase 12. The vehicle 10 further includes a battery 16 positioned onboard the base 12 of the vehicle 10 to supply electrical power tovarious operating systems present on the vehicle 10.

The battery 16 can be a rechargeable lithium-ion battery, for example,which is capable of supplying a direct current (DC) or alternatingcurrent (AC) to vehicle 10 controls, motors, actuators, and the like.The battery 16 can include at least one input 18 capable of receivingelectrical current to recharge the battery 16. In some embodiments, theinput 18 is a port capable of receiving a plug in electricalcommunication with an external power source, like a wall outlet. Thebattery 16 can be configured to receive and store electrical currentfrom one of a traditional 120 V outlet, a 240 V outlet, a 480 V outlet,an electrical power generator, or another suitable electrical powersource.

The vehicle 10 further includes a retractable lift mechanism, shown as ascissor lift mechanism 20, coupled to the base 12. The scissor liftmechanism 20 supports a work platform 22 (shown in FIG. 3). As depicted,a first end 23 of the scissor lift mechanism 20 is anchored to the base12, while a second end 24 of the scissor lift mechanism 20 supports thework platform 22. As illustrated, the scissor lift mechanism 20 isformed of a series of linked, foldable support members 25. The scissorlift mechanism 20 is selectively movable between a retracted or stowedposition (shown in FIG. 2A) and a deployed or work position (shown inFIG. 2B) using an actuator, shown as linear actuator 26. The linearactuator 26 is an electric actuator. The linear actuator 26 controls theorientation of the scissor lift mechanism 20 by selectively applyingforce to the scissor lift mechanism 20. When a sufficient force isapplied to the scissor lift mechanism 20 by the linear actuator 26, thescissor lift mechanism 20 unfolds or otherwise deploys from the stowedor retracted position into the work position. Because the work platform22 is coupled to the scissor lift mechanism 20, the work platform 22 isalso raised away from the base 12 in response to the deployment of thescissor lift mechanism 20.

As shown in FIG. 3, the vehicle 10 further includes a vehicle controller27 and a lift controller 28. The vehicle controller 27 is incommunication with the lift controller 28 and is configured to controlvarious driving systems on the vehicle 10. The lift controller 28 is incommunication with the linear actuator 26 to control the movement of thescissor lift mechanism 20. Communication between the lift controller 28and the linear actuator 26 and/or between the vehicle controller 27 andthe lift controller 28 can be provided through a hardwired connection,or through a wireless connection (e.g., Bluetooth, Internet, cloud-basedcommunication system, etc.). It should be understood that each of thevehicle controller 27 and the lift controller 28 includes variousprocessing and memory components configured to perform the variousactivities and methods described herein. For example, in some instances,each of the vehicle controller 27 and the lift controller 28 includes aprocessing circuit having a processor and a memory. The memory isconfigured to store various instructions configured to, when executed bythe processor, cause the vehicle 10 to perform the various activitiesand methods described herein.

In some embodiments, the vehicle controller 27 may be configured tolimit the drive speed of the vehicle 10 depending on a height of thework platform 22. That is, the lift controller 28 may be incommunication with a scissor angle sensor 29 configured to monitor alift angle of the bottom-most support member 25 with respect to the base12. Based on the lift angle, the lift controller 28 may determine thecurrent height of the work platform 22. Using this height, the vehiclecontroller 27 may be configured to limit or proportionally reduce thedrive speed of the vehicle 10 as the work platform 22 is raised.

As illustrated in the exemplary embodiment provided in FIGS. 4-6, thelinear actuator 26 includes a push tube assembly 30, a gear box 32, andan electric lift motor 34. The push tube assembly 30 includes aprotective outer tube 36 (shown in FIGS. 4 and 5), a push tube 38, and anut assembly 40 (shown in FIG. 6). The protective outer tube 36 has atrunnion connection portion 42 disposed at a proximal end 44 thereof.The trunnion connection portion 42 is rigidly coupled to the gear box32, thereby rigidly coupling the protective outer tube 36 to the gearbox 32. The trunnion connection portion 42 further includes a trunnionmount 45 that is configured to rotatably couple the protective outertube 36 to one of the support members 25 (as shown in FIG. 2B).

The protective outer tube 36 further includes an opening at a distal end46 thereof. The opening of the protective outer tube 36 is configured toslidably receive the push tube 38. The push tube 38 includes aconnection end, shown as trunnion mount 48, configured to rotatablycouple the push tube 38 to another one of the support members 25 (asshown in FIG. 2B). As will be discussed below, the push tube 38 isslidably movable and selectively actuatable between an extended position(shown in FIG. 2B) and a retracted position (shown in FIG. 4).

Referring now to FIG. 6, the push tube 38 is rigidly coupled to the nutassembly 40, such that motion of the nut assembly 40 results in motionof the push tube 38. The push tube 38 and the nut assembly 40 envelop acentral screw rod 50 (shown in FIG. 7). The central screw rod 50 isrotatably engaged with the gear box 32 and is configured to rotatewithin the push tube 38 and the nut assembly 40, about a central axis ofthe push tube assembly 30. The nut assembly 40 is configured to engagethe central screw rod 50 and translate the rotational motion of thecentral screw rod 50 into translational motion of the push tube 38 andthe nut assembly 40, with respect to the central screw rod 50, along thecentral axis of the push tube assembly 30.

Referring again to FIG. 4, the lift motor 34 is configured toselectively provide rotational actuation to the gear box 32. Therotational actuation from the lift motor 34 is then translated throughthe gear box 32 to selectively rotate the central screw rod 50 of thepush tube assembly 30. Accordingly, the lift motor 34 is configured toprovide rotational actuation to the central screw rod 50 via the gearbox 32. The rotation of the central screw rod 50 is then translated bythe nut assembly 40 to selectively translate the push tube 38 and thenut assembly 40 along the central axis of the push tube assembly 30.Accordingly, the lift motor 34 is configured to selectively actuate thepush tube 38 between the extended position and the retracted position.Thus, with the trunnion mount 45 of the protective outer tube 36 and thetrunnion mount 48 of the push tube 38 each rotatably coupled to theirrespective support members 25, the lift motor 34 is configured toselectively move the scissor lift mechanism 20 to various heightsbetween and including the retracted or stowed position and the deployedor work position.

The lift motor 34 may be an AC motor (e.g., synchronous, asynchronous,etc.) or a DC motor (shunt, permanent magnet, series, etc.). In someinstances, the lift motor 34 is in communication with and powered by thebattery 16. In some other instances, the lift motor 34 may receiveelectrical power from another electricity source on board the vehicle10.

Referring now to FIGS. 7-9, the nut assembly 40 includes an outer sleeve52, a primary nut mechanism, shown as ball screw nut 54, and a secondarynut mechanism, shown as a backup jam nut 56. The outer sleeve 52envelops and is rigidly coupled to both the ball screw nut 54 and thebackup jam nut 56. As such, the outer sleeve 52, the ball screw nut 54,and the backup jam nut 56 are configured to move as a unit along theaxis of the central screw rod 50.

The ball screw nut 54 is configured to engage the central screw rod 50and translate the rotational motion of the central screw rod 50 intotranslational motion of the push tube 38 and the nut assembly 40, withrespect to the central screw rod 50, along the central axis of the pushtube assembly 30. As best illustrated in FIGS. 8A and 8B, the ball screwnut 54 includes a helical thread 58 and a ball return passageway 60. Asdepicted in FIG. 8B, a plurality of balls 62 (e.g., ball bearings) aredisposed between the helical thread 58 of the ball screw nut 54 and ahelical thread 64 of the central screw rod 50. As the central screw rod50 is rotated, the plurality of balls 62 are configured to roll withinthe channel formed between the helical threads 58, 64 to gradually movethe nut assembly 40 axially with respect to the central screw rod 50, inresponse to rotation of the central screw rod 50. The ball returnpassageway 60 allows for the plurality of balls 62 to be continuouslyrecirculated from one axial location on the ball screw nut 54 to anotheraxial location, such that the plurality of balls 62 provide a continuousengagement between the helical threads 58, 64, while minimizingfrictional losses between the helical threads 58, 64.

As depicted in FIG. 9, the backup jam nut 56 includes a helical thread66. In some embodiments, the backup jam nut 56 is an Acme nut. Thehelical thread 66 is configured to normally be disengaged from thehelical thread 64 of the central screw rod 50. Specifically, the fitbetween the plurality of balls 62 and the helical threads 58, 64 createsa gap between the helical thread 66 of the backup jam nut 56 and thehelical thread 64 of the central screw rod 50. As such, under normaloperating conditions, the backup jam nut 56 does not contact orotherwise engage the central screw rod 50, and the ball screw nut 54 isthe primary nut mechanism.

However, in the event that the ball screw nut 54 fails (e.g., theplurality of balls 62 escape from the channel between the helicalthreads 58, 64 or the ball screw nut 54 is otherwise damaged), thehelical thread 66 of the backup jam nut 56 engages the helical thread 64of the central screw rod 50, providing a failsafe, backup, or secondarynut mechanism. That is, in the event of a primary nut mechanism failure(e.g., the ball screw nut 54 failing) the secondary nut mechanism (e.g.,the backup jam nut 56) is configured to engage the central screw rod 50.

The lift controller 28 is configured to detect a drive power efficiencydifference experienced by the lift motor 34 when the ball screw nut 54is engaged versus when the backup jam nut 56 is engaged. For example,when the ball screw nut 54 is engaged, the lowered frictional losses ofthe ball screw nut 54 provide a high drive power efficiency of betweenapproximately 80% and approximately 90%. Conversely, when the backup jamnut 56 is engaged, the increased frictional losses of the backup jam nut56 provide a much lower drive power efficiency of between approximately20% and approximately 30%. As such, the ball screw nut 54 requires asignificantly lower amount of power to run than the backup jam nut 56.

Accordingly, in some instances, the lift controller 28 is configured tomonitor drive power efficiency of the linear actuator 26. The liftcontroller 28 is then configured to compare the monitored drive powerefficiency to an expected drive power efficiency to determine whetherthe ball screw nut 54 is engaged or whether the backup jam nut 56 isengaged. If the lift controller 28 determines that the backup jam nut 56is engaged, the lift controller 28 may then determine that there hasbeen an actuator failure.

In some embodiments, when the ball screw nut 54 is engaged, if the liftmotor 34 is powered down or discharged, the ball screw nut 54 tends toallow the retractable lift mechanism 20 to retract due to gravity. Assuch, the lift motor 34 includes an electromagnetic brake 70 configuredto maintain the position of the work platform 22 when the lift motor 34is powered down or discharged. Conversely, when the backup jam nut 56 isengaged, the increased frictional forces may maintain the position ofthe work platform 22 without the electromagnetic brake 70. That is, thework platform 22 having a rated payload may not descend due to gravity.Accordingly, the lift motor 34 may have to actively descend the workplatform 22.

In some embodiments, the linear actuator 26 includes various built-inlift characteristic sensors configured to monitor various actuator/motoror lift characteristics. For example, the linear actuator 26 may includea motor speed sensor, a motor torque sensor, various temperaturesensors, various vibration sensors, etc. The lift controller 28 may thenbe in communication with each of these sensors, and may use real-timeinformation received/measured by the sensors to determine whether theprimary nut mechanism (e.g., the ball screw nut 54) or the secondary nutmechanism (e.g., the backup jam nut 56) are engaged with the centralscrew rod 50 (i.e., whether the linear actuator 26 has failed).

For example, in some instances, the lift controller 28 may sense thescissor arm angle using the scissor angle sensor 29 and use the scissorarm angle to determine a height of the work platform 22. The liftcontroller 28 may then process the height of the work platform 22through a lookup table to determine a maximum allowable motor torque.The lift controller 28 may then compare the maximum allowable motortorque to a required motor torque to move (e.g., raise or lower) thework platform 22. In some instances, this maximum allowable motor torqueand the required torque necessary to move the work platform 22 may bededuced using a maximum allowable current threshold to be applied to themotor and a monitored current being applied to the lift motor 34. If therequired motor torque exceeds the maximum allowable motor torque (or themonitored current exceeds the maximum allowable current threshold), thelift controller 28 may indicate that the linear actuator 26 has failed(e.g., that the primary nut mechanism has failed and that the secondarynut mechanism is engaged). The lift controller 28 is then configured toallow for the work platform 22 to be lowered to the stowed or transportposition to allow the worker or operator to safely exit the vehicle 10.Once the work platform 22 has been lowered, the lift controller 28 isconfigured to prevent continued use of the linear actuator 26 until theactuator failure has been repaired (e.g., the nut assembly 40 has beenrepaired or replaced).

Unlike with traditional hydraulics-based systems, the linear actuator 26is double-acting. That is, the linear actuator 26 can exert the samemagnitude force required to raise the work platform 22 when lowering thework platform 22. Accordingly, if the retractable lift mechanism 20encounters an obstruction while being lowered, it will exert a forceapproximately equal to the weight of the work platform 22 plus a ratedload. As such, the lift controller 28 may further be configured tomonitor the platform height, direction of movement, and actuator torque(current) to avoid structural damage.

Referring now to FIG. 10, an exemplary flow chart is provided, showingan exemplary method of use for the retractable lift mechanism 20. Theprocess starts at step 200. An operator then issues a lift command atstep 202. The machine controller or lift controller 28 then determinesthe max allowable motor torque, at step 204. As alluded to above, thismax allowable motor torque may be determined based on the height of thework platform 22. For example, the lift controller 28 may include apre-stored torque-height chart or table to be used for the max allowablemotor torque determination. The lift controller 28 then decides, at step206, whether the required torque for the lift motor 34 to lift or lowerthe work platform 22 is below the maximum allowable torque.

If the lift controller 28 decides, at step 206, that the required torqueis below the maximum allowable torque, the lift controller 28 allows thelinear actuator 26 to operate normally, at step 208. Once the commandedoperation of the linear actuator 26 has concluded, the linear actuator26 comes to a stop, at step 210.

If the lift controller 28 decides, at step 206, that the required torqueis above the maximum allowable torque, the lift controller 28 thendecides whether the work platform 22 is being commanded to ascend ordescend, at step 212.

If the lift controller 28 decides, at step 212, that the work platform22 is being commanded to ascend, the lift controller 28 then inhibitsfurther ascension and alerts the operator regarding the overloadingcondition, at step 214. The linear actuator 26 then comes to a stop, atstep 210.

If the lift controller 28 decides, at step 212, that the work platform22 is being commanded to descend, the lift controller 28 then alerts theoperator regarding the excessive motor torque, at step 216. The operatorthen checks the surroundings of the vehicle 10 and remove anyobstructions, at step 218. The operator then reissues the lift downcommand, at step 220. The lift controller 28 then again determines themaximum allowable motor torque, at step 222. The lift controller 28 thendecides, at step 224, whether the required torque for the lift motor 34to lower the work platform 22 is below the maximum allowable torque.

If the lift controller 28 decides, at step 224, that the required torqueis less than the maximum allowable torque, the lift controller 28 grantsthe linear actuator 26 normal operation, at step 208. Once the commandedoperation of the linear actuator 26 has concluded, the linear actuator26 comes to a stop, at step 210.

If the lift controller 28 decides, at step 224, that the required torqueis more than the maximum allowable torque, the lift controller 28inhibits any further lift commands and alerts operator to the actuatorfailure, at step 226. That is, once the operator has made sure there areno obstructions, if the required torque is still higher than the maximumallowable torque, the lift controller 28 may reasonably deduce thatthere has been an actuator failure. The linear actuator 26 then comes toa stop, at step 210.

The preceding process flow chart is provided as one exemplaryembodiment, and is in no way meant to be limiting. The particular orderof the process steps may be changed or added to without departing fromthe scope of this disclosure. For example, in some embodiments, the liftcontroller 28 may decide whether the work platform 22 is being commandedto ascend or descend prior to determining the maximum allowable torque.Additionally, in some instances, the exemplary flow chart may becyclical in nature, such that the flow chart returns to the start of theprocess, at step 200, after the linear actuator 26 is stopped, at step210 (as indicated by the dashed line).

In some embodiments, the lift controller 28 may additionally monitor ordetermine the require force or torque needed to lift or lower the workplatform 22, and subsequently decide whether the required force is toolow or too high to determine actuator failure.

Accordingly, the lift controller 28 is configured to determine if therequired torque needed by the lift motor 34 to lift or lower the workplatform exceeds a maximum allowed torque, to inhibit furtherfunctionality if the maximum allowed torque is exceeded to preventdamage to the vehicle 10 or the surroundings of the vehicle 10, and toalert the operator if the lift actuator is damaged and needs to bereplaced. The lift controller 28 may further monitor various liftcharacteristics to determine if the linear actuator 26 is in an unsafestate (e.g., an actuator failure state or an excessive torque state).

Referring again to FIGS. 1A and 1B, the battery 16 can also supplyelectrical power to a drive motor 72 to propel the vehicle 10. The drivemotor 72 may similarly be an AC motor (e.g., synchronous, asynchronous,etc.) or a DC motor (shunt, permanent magnet, series, etc.) for example,which receives electrical power from the battery 16 or anotherelectricity source on board the vehicle 10 and converts the electricalpower into rotational energy in a drive shaft. The drive shaft can beused to drive the wheels 14A, 14B of the vehicle 10 using atransmission. The transmission can receive torque from the drive shaftand subsequently transmit the received torque to a rear axle 74 of thevehicle 10. Rotating the rear axle 74 also rotates the rear wheels 14Aon the vehicle 10, which propels the vehicle 10.

The rear wheels 14A of the vehicle 10 can be used to drive the vehicle,while the front wheels 14B can be used to steer the vehicle 10. In someembodiments, the rear wheels 14A are rigidly coupled to the rear axle74, and are held in a constant orientation relative to the base 12 ofthe vehicle 10 (e.g., approximately aligned with an outer perimeter 76of the vehicle 10). In contrast, the front wheels 14B are pivotallycoupled to the base 12 of the vehicle 10. The wheels 14B can be rotatedrelative to the base 12 to adjust a direction of travel for the vehicle10. Specifically, the front wheels 14B can be oriented using anelectrical steering system 78. In some embodiments, the steering system78 may be completely electrical in nature, and may not include any formof hydraulics.

It should be appreciated that, while the retractable lift mechanismincluded on vehicle 10 is a scissor lift mechanism, in some instances, avehicle may be provided that alternatively includes a retractable liftmechanism in the form of a boom lift mechanism. For example, in theexemplary embodiment depicted in FIG. 11, a vehicle, shown as vehicle310, is illustrated. The vehicle 310 includes a retractable liftmechanism, shown as boom lift mechanism 320. The boom lift mechanism 320is similarly formed of a series of linked, foldable support members 325.The boom lift mechanism 320 is selectively movable between a retractedor stowed position and a deployed or work position using a plurality ofactuators 326. Each of the plurality of actuators 326 is a linearactuator similar to the linear actuator 26.

It should be further appreciated that the linear actuators used in thelift mechanism 20, 320, as well as in the steering system 78, may beincorporated into nearly any type of electric vehicle. For example, theelectric systems described herein can be incorporated into, for example,a scissor lift, an articulated boom, a telescopic boom, or any othertype of aerial work platform.

Additionally, although the depicted nut assembly 40 utilizes a primarynut mechanism in the form of the ball screw nut 54, in some embodiments,the primary nut mechanism may alternatively be a roller screw nut. Insome other embodiments, the primary nut mechanism may be any othersuitable nut for translating rotational motion of the central screw rod50 into translational motion of the push tube 38 and the nut assembly40.

Advantageously, vehicles 10, 310 may be fully-electric lift devices. Allof the electric actuators and electric motors of vehicles 10, 310 can beconfigured to perform their respective operations without requiring anyhydraulic systems, hydraulic reservoir tanks, hydraulic fluids, enginesystems, etc. That is, both vehicles 10, 310 may be completely devoid ofany hydraulic systems and/or hydraulic fluids generally. Saiddifferently, both vehicles 10, 310 may be devoid of any moving fluids.Traditional lift device vehicles do not use a fully-electric system andrequire regular maintenance to ensure that the various hydraulic systemsare operating properly. As such, the vehicles 10, 310 may use electricmotors and electric actuators, which allows for the absence ofcombustible fuels (e.g., gasoline, diesel) and/or hydraulic fluids. Assuch, the vehicles 10, 310 may be powered by batteries, such as battery16, that can be re-charged when necessary.

Although this description may discuss a specific order of method steps,the order of the steps may differ from what is outlined. Also two ormore steps may be performed concurrently or with partial concurrence.Such variation will depend on the software and hardware systems chosenand on designer choice. All such variations are within the scope of thedisclosure. Likewise, software implementations could be accomplishedwith standard programming techniques with rule-based logic and otherlogic to accomplish the various connection steps, processing steps,comparison steps, and decision steps.

As utilized herein, the terms “approximately”, “about”, “substantially”,and similar terms are intended to have a broad meaning in harmony withthe common and accepted usage by those of ordinary skill in the art towhich the subject matter of this disclosure pertains. It should beunderstood by those of skill in the art who review this disclosure thatthese terms are intended to allow a description of certain featuresdescribed and claimed without restricting the scope of these features tothe precise numerical ranges provided. Accordingly, these terms shouldbe interpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and claimedare considered to be within the scope of the invention as recited in theappended claims.

It should be noted that the term “exemplary” as used herein to describevarious embodiments is intended to indicate that such embodiments arepossible examples, representations, and/or illustrations of possibleembodiments (and such term is not intended to connote that suchembodiments are necessarily extraordinary or superlative examples).

The terms “coupled,” “connected,” and the like, as used herein, mean thejoining of two members directly or indirectly to one another. Suchjoining may be stationary (e.g., permanent, etc.) or moveable (e.g.,removable, releasable, etc.). Such joining may be achieved with the twomembers or the two members and any additional intermediate members beingintegrally formed as a single unitary body with one another or with thetwo members or the two members and any additional intermediate membersbeing attached to one another.

References herein to the positions of elements (e.g., “top,” “bottom,”“above,” “below,” “between,” etc.) are merely used to describe theorientation of various elements in the figures. It should be noted thatthe orientation of various elements may differ according to otherexemplary embodiments, and that such variations are intended to beencompassed by the present disclosure.

The hardware and data processing components used to implement thevarious processes, operations, illustrative logics, logical blocks,modules and circuits described in connection with the embodimentsdisclosed herein may be implemented or performed with a general purposesingle- or multi-chip processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. A generalpurpose processor may be a microprocessor, or, any conventionalprocessor, or state machine. A processor also may be implemented as acombination of computing devices, such as a combination of a DSP and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. The memory (e.g., memory, memory unit, storage device)may include one or more devices (e.g., RAM, ROM, Flash memory, hard diskstorage) for storing data and/or computer code for completing orfacilitating the various processes, layers and modules described in thepresent disclosure. The memory may be or include volatile memory ornon-volatile memory, and may include database components, object codecomponents, script components, or any other type of informationstructure for supporting the various activities and informationstructures described in the present disclosure. According to anexemplary embodiment, the memory is coupled to the processor to form aprocessing circuit and includes computer code for executing (e.g., bythe processor) the one or more processes described herein.

It is important to note that the construction and arrangement of theelectromechanical variable transmission as shown in the exemplaryembodiments is illustrative only. Although only a few embodiments of thepresent disclosure have been described in detail, those skilled in theart who review this disclosure will readily appreciate that manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements. It should be noted that the elements and/or assemblies ofthe components described herein may be constructed from any of a widevariety of materials that provide sufficient strength or durability, inany of a wide variety of colors, textures, and combinations.Accordingly, all such modifications are intended to be included withinthe scope of the present inventions. Other substitutions, modifications,changes, and omissions may be made in the design, operating conditions,and arrangement of the preferred and other exemplary embodiments withoutdeparting from scope of the present disclosure or from the spirit of theappended claims.

1. A lift device, comprising: a base having a plurality of wheels; aretractable lift mechanism having a first end coupled to the base andbeing moveable between an extended position and a retracted position; awork platform configured to support a load, the work platform coupled toand supported by a second end of the retractable lift mechanism; and alinear actuator configured to selectively move the retractable liftmechanism between the extended position and the retracted position, thelinear actuator comprising: a central screw rod; an electric motorconfigured to provide rotational actuation to the central screw rod; anda nut assembly comprising: a primary nut mechanism engaged with thecentral screw rod and configured to translate the rotational actuationof the central screw rod into translational motion to move theretractable lift mechanism between the extended position and theretracted position; and a secondary nut mechanism disengaged from thecentral screw rod; wherein, in an event of a primary nut mechanismfailure, the secondary nut mechanism is configured to engage the centralscrew rod.
 2. The lift device of claim 1, wherein the primary nutmechanism is a ball screw nut.
 3. The lift device of claim 2, whereinthe secondary nut mechanism is a backup jam nut.
 4. The lift device ofclaim 1, further comprising a lift controller configured to monitor atleast one lift characteristic associated with the linear actuator. 5.The lift device of claim 4, wherein the lift controller is furtherconfigured to determine whether an actuator failure has been detectedbased on the at least one lift characteristic associated with the linearactuator.
 6. The lift device of claim 5, wherein, upon determining thatthe actuator failure has been detected, the lift controller is furtherconfigured to alert an operator.
 7. The lift device of claim 6, wherein,upon determining that the actuator failure has been detected, the liftcontroller is configured to prevent further use of the linear actuatoruntil the actuator failure has been repaired.
 8. The lift device ofclaim 7, wherein the at least one lift characteristic includes a drivepower efficiency of the linear actuator and determining whether theactuator failure has been detected includes comparing the drive powerefficiency to an expected drive power efficiency.
 9. The lift device ofclaim 7, wherein the at least one lift characteristic includes a heightof the work platform and a required motor torque to move the workplatform, the lift controller is further configured to determine amaximum allowable motor torque based on the height of the work platform,and determining whether the actuator failure has been detected includescomparing the maximum allowable motor torque to the required motortorque.
 10. A lift device, comprising: a base having a plurality ofwheels; a retractable lift mechanism having a first end coupled to thebase and being moveable between an extended position and a retractedposition; a work platform configured to support a load, the workplatform coupled to and supported by a second end of the retractablelift mechanism; a linear actuator configured to selectively move theretractable lift mechanism between the extended position and theretracted position, the linear actuator comprising: a central screw rod;an electric motor configured to provide rotational actuation to thecentral screw rod; and a nut assembly comprising: a primary nutmechanism engaged with the central screw rod and configured to translatethe rotational actuation of the central screw rod into translationalmotion to move the retractable lift mechanism between the extendedposition and the retracted position; and a secondary nut mechanismdisengaged from the central screw rod; wherein, in an event of a primarynut mechanism failure, the secondary nut mechanism is configured toengage the central screw rod, and wherein the primary nut mechanism is aball screw nut; and a lift controller configured to monitor at least onelift characteristic associated with the linear actuator and to determinewhether an actuator failure has been detected based on the at least onelift characteristic associated with the linear actuator.
 11. The liftdevice of claim 10, wherein, upon determining that the actuator failurehas been detected, the lift controller is further configured to alert anoperator.
 12. The lift device of claim 11, wherein, upon determiningthat the actuator failure has been detected, the lift controller isfurther configured to prevent use of the linear actuator until theactuator failure has been repaired.
 13. The lift device of claim 12,wherein the at least one lift characteristic includes a drive powerefficiency of the linear actuator and determining whether the actuatorfailure has been detected includes comparing the drive power efficiencyto an expected drive power efficiency.
 14. The lift device of claim 12,wherein the at least one lift characteristic includes a height of thework platform and a required motor torque to move the work platform, thelift controller is further configured to determine a maximum allowablemotor torque based on the height of the work platform, and determiningwhether the actuator failure has been detected includes comparing themaximum allowable motor torque to the required motor torque. 15.(canceled)
 16. (canceled)
 17. The lift device of claim 10, wherein thesecondary nut mechanism is a backup jam nut.
 18. A lift device,comprising: a base having a plurality of wheels; a retractable liftmechanism having a first end coupled to the base and being moveablebetween an extended position and a retracted position; a work platformconfigured to support a load, the work platform coupled to and supportedby a second end of the retractable lift mechanism; a linear actuatorconfigured to selectively move the retractable lift mechanism betweenthe extended position and the retracted position, the linear actuatorcomprising: a central screw rod; an electric motor configured to providerotational actuation to the central screw rod; and a nut assemblycomprising: a primary nut mechanism engaged with the central screw rodand configured to translate the rotational actuation of the centralscrew rod into translational motion to move the retractable liftmechanism between the extended position and the retracted position; anda secondary nut mechanism disengaged from the central screw rod;wherein, in an event of a primary nut mechanism failure, the secondarynut mechanism is configured to engage the central screw rod; and a liftcontroller configured to monitor at least one lift characteristicassociated with the linear actuator and to determine whether an actuatorfailure has been detected based on the at least one lift characteristicassociated with the linear actuator.
 19. The lift device of claim 18,wherein the at least one lift characteristic includes a drive powerefficiency of the linear actuator and determining whether the actuatorfailure has been detected includes comparing the drive power efficiencyto an expected drive power efficiency.
 20. The lift device of claim 18,wherein the at least one lift characteristic includes a height of thework platform and a required motor torque to move the work platform, thelift controller is further configured to determine a maximum allowablemotor torque based on the height of the work platform, and determiningwhether the actuator failure has been detected includes comparing themaximum allowable motor torque to the required motor torque.